1. Field of the Invention
The present invention relates generally to the field of oxygen scavenging packaging. More particularly, it concerns methods and systems for initiating oxygen scavenging in an angular preformed packaging article comprising an oxygen scavenging layer.
2. Description of Related Art
It is well known that limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and shelf life of the product. For instance, by limiting the oxygen exposure of oxygen sensitive food products in a packaging system, the quality of the food product is maintained, and food spoilage is avoided. In addition, such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and restocking. In the food packaging industry, several means for limiting oxygen exposure have already been developed, including modified atmosphere packaging (MAP), vacuum packaging and oxygen barrier film packaging.
Another means for limiting oxygen exposure involves incorporating an oxygen scavenger into the packaging structure. Incorporation of a scavenger in the package can provide a uniform scavenging effect throughout the package. In addition, such incorporation can provide a means of intercepting and scavenging oxygen as it is passing through the walls of the package (herein referred to as an xe2x80x9cactive oxygen barrierxe2x80x9d), thereby maintaining the lowest possible oxygen level throughout the package. The oxygen passing through the walls may come from outside of the package or may come from inside the package.
In many cases, however, the onset of oxygen scavenging in this system may not occur for days or weeks. The delay before the onset of useful oxygen scavenging is hereinafter referred to as the induction period. Much work has been done to minimize the induction period.
Speer et al., U.S. Pat. No. 5,211,875, discloses a method for minimizing the induction period by initiating oxygen scavenging via exposure of the oxygen scavenging packaging article to radiation. The radiation can comprise UV or visible light of any wavelength from about 200 nm to about 700 nm, but preferably comprises a wavelength from about 200 nm to about 400 nm. Ching et al., U.S. Pat. No. 5,859,145, also discloses the use of UV or visible light of any wavelength from about 200 nm to about 750 nm, preferably about 200 nm to about 400 nm.
It is desirable to be able to initiate oxygen scavenging in an angular preformed packaging article that comprises an oxygen scavenging layer by exposing the interior of the packaging article to UV radiation. However, it is difficult to achieve uniform UV treatment of the interior surfaces of certain preformed, angular oxygen scavenging packaging articles with a simple UV radiation source disposed above the packaging article. Examples of such angular preformed packaging articles are gable-top cartons; parallelepiped cartons, plastic bottles, and glass bottles, among other containers. The problem of achieving relatively uniform UV exposure can become even more difficult if there is at least one non-oxygen scavenging layer between the interior of the package and the oxygen scavenging layer.
A need exists for improved methods for initiating oxygen scavenging in angular preformed packaging articles.
The present invention is directed to methods and systems for initiating oxygen scavenging in an angular preformed packaging article that comprises an oxygen scavenging layer.
One aspect of the invention is a method for initiation of oxygen scavenging in an angular preformed packaging article that comprises sidewalls, wherein the sidewalls comprise an oxygen scavenging layer. The sidewalls of the packaging article define a hollow interior and have an inner surface. The packaging article is moved into a chamber that comprises a UV exposure apparatus, and at least one of the packaging article or the UV exposure apparatus are moved relative to the other, such that at least a part of the UV exposure apparatus is positioned in the hollow interior of the packaging article. UV radiation of at least about 280 nm is emitted from the UV exposure apparatus, such that the radiation contacts the inner surface of the sidewalls of the packaging article, in a dose sufficient to initiate oxygen scavenging in the oxygen scavenging layer.
In one particular embodiment of the method, the UV exposure apparatus comprises a UV source and a member that is extendable and retractable. The member is extended to position the UV source in the hollow interior of the packaging article, where the source emits UV radiation toward the inner surface of the sidewalls. The member can subsequently be retracted.
In another particular embodiment, the UV exposure apparatus comprises a UV source and a lift mechanism. The lift mechanism moves the angular preformed packaging article such that at least a part of the UV source is positioned in the hollow interior of the packaging article, where the source emits UV radiation toward the inner surface of the sidewalls.
In yet another particular embodiment, the UV exposure apparatus comprises a UV source and a reflector apparatus for reflecting UV radiation emitted by the UV source toward the inner surface of the packaging article. The reflector apparatus is retractable and extendable. It is extended to position the reflector in the hollow interior of the packaging article. In that position, UV radiation emitted toward the reflector is then reflected toward the inner surface of the sidewalls.
In still another particular embodiment, the UV exposure apparatus comprises a UV source, a reflector apparatus for reflecting UV radiation emitted by the UV source toward the inner surface of the packaging article, and a lift mechanism for moving the packaging article relative to the reflector, such that at least a part of the reflector becomes positioned in the hollow interior of the packaging article. UV radiation is emitted from the UV source, which is reflected by the reflector toward the inner surface of the packaging article.
Another aspect of the present invention is an oxygen scavenging initiation system that comprises: (a) an angular preformed packaging article as described above; (b) a conveying apparatus for moving the packaging article into a chamber that comprises a UV exposure apparatus that emits UV radiation of at least about 280 nm; and (c) a mechanism for moving at least one of the packaging article or the UV exposure apparatus relative to the other, such that at least a part of the UV exposure apparatus is positioned in the hollow interior of the packaging article.
Examples of angular preformed packaging articles comprising an oxygen scavenging layer that can be used in the present invention include gable-top cartons, parallelepiped cartons, cups, trays, and bottles. Such angular preformed packaging articles can further comprise other layers in addition to the oxygen scavenging layer.
The oxygen scavenging layer preferably comprises an oxidizable organic compound and a photoinitiator. Examples of preferred classes of photoinitiators for use in the present invention include benzophenone derivatives containing at least two benzophenone moieties and long-wavelength UV-absorbers.
It is preferred that a UV source be selected that emits UV radiation of at least about 280 nm and at a wavelength that is optimal for absorption by the photoinitiator present in an oxygen scavenging angular preformed packaging article, leading to efficient initiation of oxygen scavenging. However, this is not always possible in practice. When the oxygen scavenging layer or certain additional layers between the oxygen scavenging layer and the hollow interior of the packaging article comprise a partially or wholly UV opaque material, the wavelength of light used should be chosen both to penetrate to and activate the oxygen scavenger. For example, when the oxygen scavenging layer comprises polyethylene terephthalate (PET), wavelengths of UV radiation greater than about 320 nm that can be absorbed by the photoinitiator should be used, as PET is opaque to shorter wavelengths of UV radiation.
As stated above, it is preferred that penetrating UV radiation of optimal wavelength for absorption by the photoinitiator present in the oxygen scavenging layer be used. When this condition is satisfied, the present invention has the advantage of maximum harvesting of the energy of the UV radiation for initiation of oxygen scavenging, thus requiring less energy input or shorter exposure times than methods known in the art. Furthermore, coupling of preferred photoinitiators in the oxygen scavenging layer of the packaging article with exposure to their optimal UV wavelength for absorption, will allow for relatively lower levels of photoinitiator to be used in the packaging article. Since photoinitiators are typically high in cost, the present invention can in some cases reduce the cost of the oxygen scavenging packaging article.
The angular preformed oxygen scavenging packaging article of the present invention is exposed to UV radiation while it passes through a chamber. Exposure of workers to UV radiation is prevented or minimized by the chamber walls. Further, the preferred wavelengths of UV radiation of the present invention (from about 280 nm to about 400 nm) are less harmful than UV radiation of certain shorter wavelengths that have been used in some previous methods of initiating oxygen scavenging in packaging. The duration of UV radiation exposure of the interior surfaces of the angular preformed packaging article should be chosen to be sufficient to achieve the desired level of oxygen scavenging initiation in the packaging article.
In addition to being used to initiate oxygen scavenging in the packaging article, the UV radiation exposure optionally can be such as to sterilize the interior surfaces of the angular preformed packaging article. Furthermore, UV radiation exposure of the interior surfaces of the angular preformed packaging article can be combined with a preceding step of wetting the interior surfaces with hydrogen peroxide. Such hydrogen peroxide wetting with subsequent UV irradiation may improve the efficiency of either initiation of oxygen scavenging or sterilization of the interior surfaces of the packaging article or both. The initiation methods and systems of the present invention can also be combined with methods of sterilizing angular preformed packaging articles (such as chemical, heat, steam, and irradiation methods).
The present invention may further comprise exposing the packaging article to a heat source which maintains its temperature at about 20xc2x0 C. to about 50xc2x0 C. while it is being treated with UV radiation to enhance initiation of oxygen scavenging.
The angular preformed packaging article of the present invention can be exposed to UV radiation for a fixed amount of time, and in such a way that the oxygen scavenging layer is relatively uniformly activated to the desired level. By bringing the oxygen scavenging layer and the UV radiation source into the necessary proximity to achieve relatively uniform activation of the oxygen scavenging layer, the present invention provides advantages over merely irradiating the article from above.
Activation of oxygen scavenging in some embodiments of the present invention can be achieved with low intensity UV radiation, thereby minimizing damage to the packaging article and maintaining safety for workers.